I really don't think a millimeter difference in thickness is going to matter to anyone. It's certainly not worth touting "worlds thinnest smartphone". Why? Because I've never seen a single uncovered iPhone4 or 4S that wasn't locked to a display table in the Apple store.

Now if reports of improved scratch resistance are true, then maybe those case will no longer be necessary. I've never used a single case on my devices and they hold up remarkably well (Nexus S, and Galaxy Nexus). But that probably won't stop most iPhone 5 buyers from slapping on a "protective" case thus making 1mm difference rather inconsequential.

I actually prefer my iPhone 4 without a case. But sometimes I like to "dress it up". And other times... it's just because I'm a major klutz, and I'm trying to prevent the corners from getting even more dinged up.﻿